1. Field of the Invention
The invention relates to a signal recording apparatus and, more particularly, to an apparatus for digitally recording an audio signal and a video signal.
2. Related Background Art
Hitherto, for instance, as a digital video tape recorder (VTR), there are considered a VTR of the type in which a recording area (video area) for a video signal and a recording area (audio area) for an audio signal are separately provided on a recording track of a tape, both the video and audio signals are processed by signal processing circuits provided separately and the recording and reproduction are executed, and a VTR of the type in which both the video signal and the audio signal are recorded into the same area (video area). In the digital VTR of any of the above two types, there is known an apparatus in which the left channel (LCH) signal and the right channel (RCH) signal of the stereophonic audio signal are recorded and reproduced for every channel, and a subarea is provided to enable after recording of an audio signal into the subarea.
In the conventional VTR of the analog recording and reproducing system, a VTR having not only the standard recording mode but also the long playing mode whose recording time is longer than that in the standard recording mode is known. A method of realizing the two modes even in the VTR of the digital recording and reproducing system is considered. That is, in the digital VTR, digital signals are recorded at a track pitch at which the lowest allowable S/N ratio that enables reproduction is obtained and the track pitch itself cannot be changed. In the digital VTR, therefore, in the long playing mode, an amount of digital data to be recorded is reduced (band compression) to an amount smaller than that in the standard mode, thereby coping with such a long playing mode. For instance, an amount of information which is recorded per unit time is changed every mode in a manner such that a track pattern as shown in FIG. 1A is formed in the standard mode using two pairs of heads (total of four heads) which are attached to the outer periphery of a rotary cylinder in a manner such that each pair of heads have a phase difference of 180.degree. and that a track pattern as shown in FIG. 1B is formed in the 1/2 speed mode (i.e., double recording time mode). In FIG. 1, the recording tracks are shown on the assumption that the track on/from which a signal is recorded and reproduced by one of the heads of one pair is set to TA+, the track on/from which a signal is recorded and reproduced by the other head of the above pair is set to TA-, the track on/from which a signal is recorded and reproduced by one of the heads of the other pair is set to TB+, and the track on/from which a signal is recorded and reproduced by the other head of the above other pair is set to TB-, respectively.
In the above conventional apparatus, however, the information amount of the image signal is compressed into a fraction of an integer but an information amount of the audio signal is not compressed. Therefore, for instance, assuming that an area to record the audio signals of two channels is assured in the same area as that of the image signal and an area to record the audio signals of two channels is assured in the subarea for the after recording in the standard mode, only the audio signal of one channel can be recorded in the same area as that of the image signal and only the audio signal of one channel can be recorded in the subarea for the after recording in the long playing mode in which the double recording time is obtained. Now, assuming that the left or right signal of the stereophonic audio signal has been recorded into the same area as that of the image signal and the right or left signal has been recorded into the subarea for the after recording in the long playing mode, when the after recording is executed for the above recorded tape, the information on either the right or left side of the stereophonic audio signal drops out, so that an unnatural reproduction signal is derived.